No Index Tag pages? Thoughts? Advice?

Took over SEO for a local small business company. For some targeted keywords the solid landing pages are not ranking, but some BS pages and tag pages are. I have seen their impressions jump up quite a bit since we were working with them, but with that their CTR decreased (we're pushing a lot of content). In any event, what's your general thought of no-indexing tag pages? Always no-index? Dependent? If so, why? And what about one where they may be ranking? Thanks.